Cellular mechanisms of epileptogenesis will be studied in acute penicillin foci of cats and in in vitro neocortical and hippocampal slices. Potential contributions of dendritic spike generation in normal neurons and those generating depolarization shifts (DSs) after exposure to penicillin will be examied. Hyperpolarizations which occur after spike trains or after DSs will be studied to determine potential contributions of changes in potassium conductance versus IPSPs. Measurements of alterations in extracellular ionic concentrations of Cl-, Ca ions and K ions will be made in vivo and in vitro during epileptogenesis using ion sensitive microelectrodes. Mechanisms of antidromic burst generation in cortical axons will be examined. The effects of barbiturates (phenobarbital and pentobarbital) on synaptic activities and other properties of hippocampal neurons will be evaluated.